When connecting like devices by way of a cable, current called surge current may flow in a signal line or ground line due to the ground potential difference of like devices or the potential difference from electrical charge accumulation such as electrostatic charge. A driver device on the transmission side or receiver device on the receiving side provided inside the device may be damaged from this surge current flowing therein.
Conventionally, a protection diode has been used in order to prevent device damage arising from surge current. By connecting a protection diode between a signal line or ground line and the power source, it is possible to release the surge current to the power source. A Schottky diode, varistor or the like have been used as protection diodes.
By providing a protection diode, it is possible to prevent a device from being damaged by this surge current to some extent. However, the possibility for latch-up to occur in the device cannot be completely eliminated. When latch-up occurs in a device, excessive current flows between the positive-side power voltage and the ground-side power voltage of the device, and thus the device generates heat and is damaged by this excessive current.
As an example of a protection circuit against excessive current, Patent Literature 1 discloses a configuration that generates supply voltage to be supplied to a CPU by way of a three-phase voltage supply circuit, in which the configuration provides a resettable fuse on the power voltage side of power control modules of the respective three phases. More specifically, modules that alternately turn ON and OFF MOSFETs on a high (HIGH) side and low (LOW) side to generate a PWM waveform are provided in the three phases, and the outputs of the three-phase are coupled thereto, further smoothed with an inductor and capacitor, and then supplied as power voltage to a CPU. In this configuration, a resettable fuse is inserted in each of the three paths supplying power voltage to the three modules generating PWM waveforms.
With the technology described in Patent Literature 1, the resettable fuses (70, 71, 72) are arranged just before the voltage control modules (20, 30, 40), and are not directly connected to the CPU (60); therefore, latch-up of the CPU cannot be prevented.
Patent Literature 2 discloses a configuration providing a latch-up protection circuit in a path supplying power voltage to an internal circuit of an integrated-circuit chip. This latch-up protection circuit switches OFF an on-chip voltage regulator supplying electric power to the internal circuit if the current supplied to the internal circuit exceeds a predetermined set value. This configuration is a configuration that has a circuit for latch-up protection built into the integrated-circuit chip, whereby an IC element equipped with a latch-up protection function is provided.
With the technology described in Patent Literature 2, there is a problem in that it is necessary to build the latch-up protection circuit into the integrated-circuit chip in advance, and it cannot be applied to an integrated-circuit without a latch-up protection circuit built in. In addition, building the latch-up protection circuit into the integrated-circuit leads to increased costs in the design of the integrated-circuit and fabrication steps.